During the production of secondary amines, primary amines can also be produced. For example, in the production of piperidine, n-amylamine is also produced. Often times, customers demand that secondary amine products contain very small quantities of primary amine. For example, product specifications for the amount of n-amylamine in piperidine can be as low as 0.1% by weight. Removing primary amines from secondary amines is not a simple process since the boiling points of primary amines and secondary amines of similar molecular weight can vary by only a few degrees Celsius. For example, the boiling point of n-amylamine is 104.degree. C. while the boiling point of piperidine is 106.degree. C.
Several chemical reaction schemes have been proposed to remove primary amines from secondary amines. One such reaction scheme involves a reaction of an aldehyde or ketone with a primary amine to form an "imine". This reaction scheme may be represented by: ##STR1## where R.sub.1 and R.sub.2 can be the same or different and are selected from the group consisting of hydrocarbyl radicals having from 1 to about 10 carbon atoms per radical. This reaction is reversible, and the water must be removed to drive the reaction to completion. One method of removing the water is to add benzene or cyclohexane to high boiling ketones to azeotrope with water. Then, the secondary amine can be removed by distillation. This reaction scheme is cumbersome due to the requirement of removing water and the difficulty in separating the imine and aldehyde or ketone from the secondary amine. Furthermore, secondary amines can react with the aldehyde or ketone in an equilibrium reaction lowering the amount of secondary amine produced.
A process is needed to efficiently separate primary amines from secondary amines. This invention provides such a process.